I HAVE PURCHASED THIS PRODUCT FROM MTS STORE BUT THERE I AM FACING RINGER PROBLEM, (IF WE CHANGE SD CARD OR SIM THAN IT BECOME SILENT FOR MINIMUM 5 DAYS , NO OUTPUT OF VOICE EXISTS THROUGH ITS PHONE SPEAKER IN ANY MODE, EITHER WE TRY YOUTUBE OR SD CARD MUSIC FILE OR ANY OTHER RINGTONE OF THE PHONE, IT JUST VIBRATE)